Projection exposure machines are used for the photo-lithographic production of semiconductor components and other finely structured components. Their performance is substantially determined by the imaging properties of the projection optics. The image quality and the wafer throughput achievable with a machine are determined substantially by properties of the illumination system based upstream of the projection objective. In a projection exposure machine the pattern of a mask reticle is projected onto an object coated with a photo-sensitive layer, with maximum resolution on a reducing scale. In order to be able to generate finer and finer structures, attempts are made to constantly increase the numerical aperture (NA) on the image side of the projection objective, wherein values of NA=0.7 or more are achievable at present. Furthermore, shorter and shorter wavelengths in the deep ultra-violet (DUV) range or in the vacuum ultra-violet (VUV) range are being used.
In projection exposure machines used in the past, the illumination light could be regarded more or less as scalar light. Under conditions of short wavelengths and high numerical apertures, however, the influence of polarization effects on the imaging quality becomes increasingly important. With high numerical apertures, for example, at values of NA=0.85 or more, the vector character of the image-generating electric field becomes increasingly significant. It has been found, for example, that the s-polarized component of the electric field, i.e., the component which oscillates perpendicularly to the incidence plane spanned by the incidence direction and the surface normal of the substrate, interferes better and generates better contrast than the p-polarized component, oscillating perpendicularly to it. On the other hand, p-polarized light generally enters the photoresist better.
Therefore, it becomes more and more important to gain prior knowledge about imaging results to be expected in an optical imaging process when applying a particular optical radiation field to the process. In particular, it is desirable to gain knowledge about configurations of destructive interference of the optical waves or partial optical waves of an optical radiation filed for the selection of optimal adjustments of illumination parameters and for the determination of critical layout situations.